Fossil Record

The fossil record of the Crustacea is exceptionally
good, stretching back to the Cambrian. However,
they don't appear in any abundance until the Carboniferous.

The first undisputed crustaceans are Canadaspis and
Perspicaris which belong to the Subclass Phyllocarida and
were found in the Middle Cambrian Burgess Shale.

By the Carboniferous, all the other major groups of crustaceans
are present except for the Eucarida. Most
of these fossils are found within shallow marine sediments because
these offered good potential for preservation. The Eucarida
appeared in the Mesozoic, but they had their origins
in the Devonian/Carboniferous. The Eucarida, especially the Decapoda,
underwent an adaptive radiation during the Jurassic, with the appearence
of crabs and modern shrimps.

Canadapsis perfecta
is one of the earliest crustaceans from the Middle Cambrian of the Burgess
Shale. Copyright Smithsonian Institution.

The crabs and lobsters carried on diversifing to become one
of the major groups of marine organisms. Hermit crabs are an unusual
group that seek protection inside discarded mollusc shells. Hermit crabs are known
at least from the Cretaceous Speeton Clay where hermit crabs inhabited empty ammonite shells.

Cretaceous hermit crab within an
ammonite shell. A-B left and right side of the inhabited ammonite.
C-E different apertural views with the hermit crab Palaeopagurus
vandenegeli within it. Image taken from Palaeontology vol
46 part 1, 2003.

Artist's reconstruction of P.
vandenegeli living within the ammonite shell. Taken from Palaeontology
vol 46 part 1, 2003.

The ostracods, which have a fossil record going back to the Cambrian,
are commonly found in sediments of all ages. They are so abundant
that they can be used in biostratigraphy and show such a range
of environmentally-dependent morphologies that past ocean temperatures
can be calulated from them. On the right is a picture of a marine ostracod.

In Tertiary sediments the barnacles started to
appear in abundance. This was the group that Charles Darwin
studied in great taxonomic detail before embarking upon the Origin of
Species. On the left is a picture of some fossil barnacles.